An organic light-emitting device, which is generally called as EL (Electroluminescence device), is one of the representative flat-panel display devices along with Liquid Crystal Display (LCD), Plasma Display Panel (PDP), and Field Emission Display (FED). The organic light-emitting device does not require a back-light for light-emitting, and can be manufactured into a thin film and flexible type device, and mass-produced by the well-known film fabrication techniques. In addition, the EL is a self-light emitting device. Therefore, the EL has not only a fast response speed but also an excellent brightness and wide viewing angle. Also, the EL can be operated with a low driving voltage, and display full colors in a visible region.
In the organic light-emitting device, an organic light-emitting layer having a light-emitting property is interposed between a transparent electrode made of ITO having a high work function and a metal electrode made of Mg having a low work function. When a voltage is applied to the electrodes, holes and electrons are generated at the electrodes, and recombined at the organic light-emitting layer to induce a light-emission. To produce a full-color organic light-emitting device, it is necessary to prepare organic light-emitting compounds for emitting red (R), green (G) or blue (B) light. Such organic light-emitting compounds are disclosed in various references, for example, U.S. Pat. Nos. 3,852,683, 3,986,140, 4,012,376, 4,146,707, 4,769,292, 5,018,160, 5,294,869, 5,409,783, 5,492,942, 5,908,581, and 5,935,720, “Design and Synthesis of Red Dopants for Electroluminescence” (C. H. Chen and C. W. Tang, Chemistry of Functional Dyes, Vol. 2, pp. 536–543 (1993)), “Electroluminescence of Doped Organic Thin Films” (C. W. Tang, S. A. VanSlyke, and C. H. Chen, Journal of Applied Physics, Vol. 65, pp. 3610–3616 (1989)), “Red-light-emitting organic electroluminescent devices with bisanil dye as emitter” (Junsheng YU, Zhijian CHEN, and Seizo MIYATA, Jpn. J. Appl. phys. Vol. 40(2001) pp. 3201–3205) et al.
Among the organic light-emitting compounds, 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM), which emits the light having the wavelength of 590 nm, and 4-dicyanomethylene-6-cp-julolidinostyryl-2-tert-butyl-4H-pyran (DCJTB), which emits the light having the wavelength of 630 nm and is one of the derivatives of DCM, are conventionally used as the red organic light-emitting compound. The red organic light-emitting compound having the DCM structure is produced by substituting a substituent, such as alkyl group, to nitrogen. Therefore, the compound having the DCM structure has a low heat resistance, which results in the decrease of the life span of the organic light-emitting device.